High frequency power transformers and inductors used in power supplies, such as in the power supplies for cathode ray tube (CRT) displays generally radiate strong electromagnetic fields. However, as the frequency of operation of the transformers is frequently the same as the horizontal deflection frequency of the CRT, the visible effects are frequently minimal. Unfortunately, the operating frequency of efficient power supplies can no longer keep up with the increasingly high deflection frequencies encountered in the high scanning rate ultra-high resolution CRT display. Thus, the power supplies are forced to operate at a frequency below the scanning rate of the CRT. Operating the power supply at an exact sub-multiple of the scanning frequency still causes significant distortion in the CRT image due to the radiating magnetic field of the power transformer, which dramatically increases as the frequency of operation of the power supply increases.
Heretofore, shielding of the high frequency power transformer has been largely limited to encasing the entire transformer in a tightly sealed metal box, sometimes including the drive electronics. Potential flashover (arcing) between the high voltage windings and the metal box were avoided by providing generous air spacing between the transformer and the box. However, the box shielding of electromagnetic radiation is often insufficient and requires significant area within the CRT display. Alternately, the transformer is potted in a high voltage insulating material (also typically having a high dielectric constant) to form a single, void-free structure. However, displacement current in the transformer encapsulation material such as a plastic (typically epoxy) develops a high potential on the surface, frequently arcing through the air (having a lower dielectric constant) to a surface of sufficiently different potential, such as the other side of the void or slightly spaced metal structures. Significant difficulties also arise in the manufacture of truly void-free structures.